sm82s1215-4751

INTRODUCTIONTop Mediterranean demersal fisheries are characterized by a critical combination of high fishing effort and low size at first capture of commercial species (, , ). This is mainly due to the progressive growth in engine power of trawlers, the rapid technological advances in fish finding and fishing technology, and the traditional use of fine mesh size in the cod-end (). Due to its low selectivity, Mediterranean bottom trawling produces a high amount of discards and, although several technical solutions have been developed for discard reduction (e.g. , , ), the management measures adopted have been mostly limited to increasing the mesh size in the cod-end (e.g. ). In 2006, a specific regulation for the management of Mediterranean fisheries was approved by the European Union (Reg. UE 1967/2006), emphasizing the importance of the Mediterranean basin for the Common Fishery Policy (CFP). In this regulation, a set of measures were adopted to improve the sustainable exploitation of Mediterranean stocks. In particular, minimum conservation reference sizes (MCRS) were defined for the most important species, in addition to a minimum legal mesh size in the trawl net cod-end of 40-mm square mesh or 50-mm diamond mesh. Over the last decade, the reduction of discarding of the non-commercial fraction in fisheries has become an increasingly important objective from the socioeconomic, ecological, and moral point of view (, , ). The CFP has defined specific management measures to reduce discarding of catches of regulated species, including the landing obligation (Article 15 of EU Reg. 1380/2013) of all Mediterranean species subject to MCRS (). These species include the deep-water rose shrimp (DPS), Parapenaeus longirostris (Lucas, 1846), and the European hake (HKE), Merluccius merluccius (Linnaeus, 1758). The DPS is one of the main target species of trawl fishery in several Mediterranean sectors and represents about 40% of total trawl landing in the Strait of Sicily (central Mediterranean) (). In this area, DPS is caught by trawl vessels fishing on the outer continental shelf and upper slope in geographical sub-areas (GSAs) 12 (northern Tunisia), 13 (Gulf of Hammamet), 14 (Gulf of Gabes), 15 (Malta) and 16 (Southern Sicily). The available scientific information indicates that fishing fleets of Italy, Malta and Tunisia exploit a single shared DPS stock () with a total catch of about 7540 t in 2016. This catch is mostly due to the Italian (70%) and Tunisian (30%) vessels, the Maltese yield being negligible. The main commercial species associated with DPS trawling is the European hake (Merluccius merluccius; HKE), amounting to about 10% of the total trawl landing. According to , the annual discards due to DPS trawl fisheries in the Strait of Sicily accounted for about 36% of the total catch. This fraction also included undersized specimens of species under MCRS according to Reg. UE 1967/2006, such as DPS and HKE, which are consequently subject to the European discard ban. Reducing discards in multi-species trawling (, ) is a main challenge in Mediterranean fisheries. In fact, the legal mesh size adopted is suitable for catching crustaceans, cephalopods and medium-size fish such as red mullets, but it is too small to avoid the catch of juveniles of large-sized fish such as hake and monkfish (). For the latter species, the adoption of a bigger cod-end mesh size would be required to increase their size of first capture, as observed in numerous experiments carried out in Mediterranean waters testing different combinations of mesh geometry and mesh size in the trawl cod-end (, and references herein). However, a significant mesh size increase would easily break up the current catch profile of Mediterranean bottom trawlers, with a significant loss of small-sized marketable species and individuals of other commercial species (e.g. ). Alternative selection tools and technical solutions to the classical mesh size increase in the cod-end have proved to be effective in improving trawl selectivity without a major loss of commercial fish and shellfish (e.g. , , ). These include changes in the cod-end circumference (), the use of square-mesh panels inserted in front of the cod-end (e.g. ) and the adoption of sorting grids (, , ). In particular, the studies carried out on sorting grids have revealed clear advantages associated with their use in mixed trawl fisheries, such as improved selectivity and by-catch reduction (e.g. , ), a stable selection pattern during the tow (), and a higher survival rate of specimens escaping from the grid bars compared with a conventional cod-end mesh (e.g. , ). The main disadvantages are related to handling on board trawl nets equipped with grids, the potential occlusion of the grids by debris, and their sporadic reduced sorting capacity when a high number of fish arrive simultaneously (). Although all these studies point to the positive impact of sorting grids on the size at first capture of commercial fish and crustaceans (e.g. , ), their adoption in Mediterranean trawl fisheries is still very low. Lack of sorting grid implementation could be linked to several causes, including fishers’ resistence to changing fishing traditions and customs, and, consequently their unwillngness to modify their fishing gear substantially. Other possible causes are linked to the lack of a suitable technology transfer from researchers to fishing enterprises (e.g. ), as well as the overall weakness of fishing management in the Mediterranean region (). In this study we tested the efficiency of sorting grids in improving the selectivity of trawlers targeting DPS in the Strait of Sicily. Three different types of sorting grids were designed in collaboration with some trawl vessel captains of the Mazara del Vallo fleet and tested during ad hoc designed fishing trials. The objective of the study was to quantify the effects of the sorting grids on the catch of undersized specimens of DPS and HKE and to elucidate both the technical constraints and the possible trade-offs in terms of fishery sustainability. MATERIALS AND METHODSTop Study area The study area, located in the northern part of the Strait of Sicily [GSA 16 of the General Fishery Council for the Mediterranean (GFCM); Fig. 1] off the southwestern coast of Sicily, is characterized by a wide continental shelf with an intense hydrographic circulation pattern, a stable upwelling system and high biodiversity (). These abiotic and biotic features lead to a high productivity of fish resources which are exploited by a multinational fleet in national and international waters. In the Italian fleet, DPS is mainly exploited by about 240 bottom trawlers larger than 18 m length overall (LOA), mostly located in the ports of Mazara del Vallo, Sciacca and Porto Palo di Capo Passero, with an operational depth range of 100 to 400 m.

Full size image

Fig. 1. – The study area highlighted with a black square box.

Sorting grids trials A six-day trawl survey was organized by hiring a local commercial bottom trawler registered in the harbour of Mazara del Vallo with an LOA of 21.5 m and engine power of 316 kW. The trawler was equipped with a traditional polyamide trawl net with a nominal mesh cod-end size of 40-mm square mesh. The net design had a nominal mesh size of 50-mm diamond mesh in the extension section and the following characteristics: 305 meshes in the extension circumference, 210 meshes around the cod-end circumference and 125 meshes in the cod-end length. Three different types of juvenile and trash excluder devices (JTEDs) were designed to be installed on the trawl net and tested during the survey. JTEDs were based on the configuration proposed by , including a funnel panel specifically adapted to the characteristics of the local trawl nets. An interchangeable system was designed to adapt the grids on a fixed frame. It was characterized by a main steel frame fixed on the extension section of the net, on which the three different grids were fixed (Fig. 2). The grids differed in both their material and bar spacing. The first grid type (G1-SM40) was built with a net of 40-mm square mesh while the second (G2-ST20) and third (G3-ST25) were made from vertical steel bars spaced 20 and 25 mm apart, respectively (see Fig. 2).

Full size image

Fig. 2. – The designed sorting grid (JTED) with two parts: A, interchangeable grids in a steel frame; B, the fixed steel frame.

Sampling design and data analysis The sampling design was based on 36 trawl hauls of 1 hour carried out during day and night on six days between late October and early Novemeber 2015 at a constant trawling speed of about 3 knots and between 100 and 130 m. Although the trial was planned for six consecutive days, after the fourth day the experiment was suspended due to adverse weather conditions. Half the hauls were carried out using JTEDs (6 hauls for each JTED type) installed on the net and the other 18 hauls (control) were repeated without JTEDs at the same depths and geographical positions (Table 1).

Table 1. – Days, number of repeated hauls, geographic coordinate and mean depth for each designed JTED and its relative control in the experimental survey. G1-SM40, JTED covered with a net of 40-mm square mesh; G2-ST20, JTED with steel bars spaced 20 mm; G3-ST25, JTED with steel bars spaced 25 mm.

Data	28/10/15	29/10/15	30/10/15	31/10/15	6/11/15	7/11/15	Haul	Time (start)	Time (end)	Lat. (start)	Long. (start)	Lat. (end)	Long. (end)	Mean depth (m)
Design	control	G1-SM40	control	G2-ST20	control	G3-ST25	1	13:30	14:30	37°27′62″	12°26′37″	37°27′16″	12°26′07″	110
							2	17:30	18:30	37°23′58″	12°24′78″	37°23′10″	12°24′65″	120
							3	21:30	22:30	37°17′40″	12°25′11″	37°17′75″	12°25′13″	126
							4	01:30	02:30	37°22′51″	12°24′80″	37°22′83″	12°24′94″	123
							5	05:30	06:30	37°27′26″	12°33′46″	37°27′16″	12°34′35″	98
							6	09:30	10:30	37°29′08″	12°28′55″	37°28′49″	12°29′22″	100

All specimens of DPS and HKE were measured, and those below MCRS, i.e. 20 mm carapace length for DPS and 20 cm total length for HKE, were identified as undersized (US). To assess change in the length composition of catch obtained with and without JTED a model able to fit a continuous curve along the length classes was preferred to the traditional paired tests by length classes (, ). As a first step, we estimated the probability of retaining a fish at length in the JTED trawl related to the total catch in the control (trawl net without JTED) according to the method proposed by and for experimental paired hauls. Since it was not possible to hire two fishing vessels and a paired haul sampling design, we assumed the same catch probability for JTED and control hauls carried out at the same time of day, depth and geographical position. This assumption was corroborated by the absence of statistical differences in length frequency distributions among the control hauls (Kolmogorov-Smirnov test, p>0.05). According to , the probability, P_St, of catching specimens of the size class “S” at the daytime “t” was computed as

P_{St} = \frac{S_{t} with JTED}{S_{t} {with JTED + S}_{t} without JTED}

In this context, P_St is an estimate of the observed catch efficiency for each size class with JTED in comparison with without JTED. A P_St value of 0.5 indicates lack of difference in the selectivity between trawl nets with (test) and without (control) JTED. P_St>0.5 means a catch of size class S that is higher in the test than in the control, whereas the opposite occurs with P_St<0.5. P_St values of 0.33 and 0.66 correspond, for example, to a catch difference of –50% and +50%, respectively, between test and control.

The observed P_St values of DPS and HKE of each JTED type were modelled using GAMMs, where haul time was treated as random effects to remove the variance linked to the expected change in abundance/catchability of the two species during the day (Holst and Revill 2009Holst R., Revill A.S. 2009. A simple statistical method for catch comparison studies. Fish. Res. 95: 254-259.). The final GAMMs were preferred to generalized linear models and generalized additive models based on normal residual distribution, explained variance and the Aikake information criterion (Zuur et al. 2007Zuur A.F., Ieno E.N., Smith G.M. 2007. Analysing Ecological Data. Springer-Verlag, New York, 672 pp.). The statistical analysis was performed using the R package mgcv (Wood 2006Wood S.N. 2006. Generalized additive models: an introduction with R. Chapman & Hall, Boca Raton, Florida, U.S.A., 416 pp.).

Finally, in order to better visualize the grid efficiency according to the behaviour of the investigated species, the relative proportion of undersized species, P_us, in the catch was calculated separately for day- and nighttime hauls as well as for JTED type, as

$P_{us} = \frac{Σ n_{us} test}{Σ n_{us} test + Σ n_{us} ctrl}$

where, n_us is the number of speciems below the MCRS.

RESULTSTop

The absolute number of specimens caught between test and control was significantly different only for DPS (test=5691; control=9970), while for HKE no significant difference was found (test=1566; control=1569) (Fig. 3). The length frequency distributions of DPS and HKE showed a similar shape between test and control. However, the proportion of undersized specimens was lower in test hauls, with clear differences between the two species. In the case of DPS, mainly G1-SM40 led to a reduction in the catch of shrimps of less than 20 mm carapace length (CL) (–6%), while all three grids produced less catch of HKE <20 cm TL (G1-SM40 –20%; G2-ST20 –6%; G3ST25 –7%) compared with the control (Fig. 3).

Full size image

Fig. 3. – Comparison of the length frequency distributions of deep-water rose shrimp (DPS; left) and European hake (HKE; right), retained in the cod-end during the hauls with JTEDs (dashed line) and without grids (control [ctrl], solid line).

The parameters and R² of the fitted mean probability functions of the final GAMMs are presented in Table 2. The GAMM for JTED G1-SM40 showed that the estimated P_St of DPS increased from 0 to 0.3 for shrimps between 10 and 18 mm CL, corresponding to a decrease in catch probability of 100% to 60% compared with the control. P_St appeared constant at about 0.3 for 18-25 mm CL DPS, increasing progressively up to 0.5 (no differences from the control) for 30 mm CL shrimps (Fig. 4). In the case of HKE, the estimated P_St ranged between 0.2 and 0.5 for 15-20 cm TL, although with a higher uncertainty due to the low catch. P_St increased up to 0.6 for 20-24 cm TL, but over this size there was no clear significant catch effect of the grid (Fig. 5). The estimated P_Stvalues using G2-ST20 for DPS were quite similar to those obtained with G1-SM40. In fact, the P_St increased from 0 to 0.3 for shrimps between 9 and 18 mm CL (decreasing in catch probability between 100% and 60% compared with the control), remained quite costant at about 0.28 between 18 and 23 mm CL, and after that, size increased progressively up to 0.5 (no differences from the control) at 27 mm CL (Fig. 4). In the case of HKE, P_Stranged between 0.4 and 0.5 for 10-21 cm TL (decreasing catch probability by up to 20% compared with the control), increased to 0.6 (increasing the catch probability by up to 20% compared with the control) for 15-26 cm TL, and after that size there was high uncertainty due to the low catch (Fig. 5). With G3-ST25 the estimated DPS P_St values ranged between 0.1 and 0.2 for 10-20 mm CL (decreasing catch probability by up to 69% compared with the control), and after this size the P_Stincreased slowly to 0.6 for 20-30 mm CL. The estimated P_St HKE ranged between 0.3 and 0.5 for 10-20 cm TL (decreasing catch probability by up to 35% compared with the control), and over this size there was no clear significant catch effect of the grid (Fig. 5).

Table 2. – GAMM parameters from comparison of trawl net equipped with JTED (test gear) with trawl net without JTED (control gear) with catch in number per hour. G1-SM40, JTED covered with a net of 40-mm square mesh; G2-ST20, JTED with steel bars spaced 20 mm; G3-ST25, JTED with steel bars spaced 25 mm.

Comparison	Species	DF	R square	F statistic	p-value
G1-SM40 vs control	DPS	7.99	0.21	9.963	<0.001
G1-SM40 vs control	HKE	4.56	0.23	5.507	<0.001
G2-ST20 vs control	DPS	7.38	0.11	13.05	<0.001
G2-ST20 vs control	HKE	5.64	0.11	12.85	<0.001
G3-ST25 vs control	DPS	5.02	0.10	4.013	<0.001
G3-ST25 vs control	HKE	5.94	0.24	13.6	<0.001

Full size image

Fig. 4. – Proportion of fish retained in trawl nets equipped with JTEDs (=JTED/(JTED+ control) vs. length for deep-water rose shrimp (DPS). The value of 0.5 means both gears catch equal numbers,the solid line gives the mean, and the grey band gives the 95% confidence limit. MCRS (DPS, 20 mm; HKE, 20 cm). G1-SM40, JTED covered with a net of 40-mm square mesh; G2-ST20, JTED with steel bars spaced 20 mm; G3-ST25, JTED with steel bars spaced 25 mm.

Full size image

Fig. 5. – Proportion of fish retained in trawl nets equipped with JTEDs (=JTED/(JTED+ control) vs. length for European hake (HKE). The value of 0.5 means both gears catch equal numbers,the solid line gives the mean, and the grey band gives the 95% confidence limit. MCRS (DPS, 20 mm; HKE, 20 cm). G1-SM40, JTED covered with a net of 40-mm square mesh; G2-ST20, JTED with steel bars spaced 20 mm; G3-ST25, JTED with steel bars spaced 25 mm.

The P_us values with G1-SM40 were 0.37 and 0.19 for DPS and 0.25 and 0.51 for HKE during the diurnal and nocturnal hauls, respectiPvely (Table 3). For G2-ST20 the P_us values during the diurnal and nocturnal hauls were 0.38 and 0.16 for DPS and 0.40 and 0.47 for HKE, respectively. Similarly, with G3-ST25 the P_us values during the diurnal and nocturnal hauls were 0.33 and 0.18 for DPS and 0.48 and 0.44 for HKE, respectively. These values were similar between diurnal (0.37, 0.38 and 0.33) and nocturnal hauls (0.19, 0.16 and 0.18) for DPS, clearly showing an efficient reduction of undersized shrimp catch in the cod-end of ~45% in daytime and ~73% at nighttime, compared with the control. The P_us for HKE were different (0.25, 0.40 and 0.48) during the diurnal hauls, showing a reduction of undersized hake of 0.38% to 72%, while were close to 0.5 during the nocturnal hauls (0.51, 0.47 and 0.46) showing no differences in the retention of undersized HKE between test and control at night (Table 3).

Table 3. – Probability of undersized specimens of deep-water rose shrimp (DPS) and European hake (HKE), recorded during the daily and nightly hauls with and without JTEDs. G1-SM40, JTED covered with a net of 40-mm square mesh; G2-ST20, JTED with steel bars spaced 20 mm; G3-ST25, JTED with steel bars spaced 25 mm.

Haul	Grid type	DPS Probability of undersize	sd	HKE Probability of undersize	sd
day	G1-SM40	0.37	0.13	0.25	0.04
night	G1-SM40	0.19	0.09	0.51	0.27
day	G2-ST 20	0.38	0.11	0.40	0.04
night	G2-ST 20	0.16	0.13	0.47	0.11
day	G3-ST 25	0.33	0.12	0.48	0.12
night	G3-ST 25	0.18	0.09	0.44	0.11

DISCUSSIONTop

The results of our catch comparison experiment showed that the use of JTEDs mounted on traditional trawl nets of Mediterranean trawlers can be beneficial in reducing the by-catch of undersized individuals (i.e. individuals below the MCRS) of two important commercial species, the deep-water rose shrimp and the European hake. The three different types of JTEDs that were tested produced significant and sometimes contrasting differences in the catch of small individuals of the two species. The JTED consisting of a stretched square mesh size of 40 mm (G1-SM40) produced a high sorting ability for both species in terms of reduction of juvenile catch (DPS –60%, P̅_St=0.26; HKE –44%, P̅_St=0.37) with a minor loss of the marketable fraction for DPS (DPS –25%, P̅_St=0.48; HKE –39%; P̅_St=0.40).

The results clearly demostrated also the good efficiency in reduction of undersized specimens using G2-ST20 (DPS –59%, P̅_St=0.27; HKE –34%, P̅_St=0.43) and G3-ST25 (DPS –73%, P̅_St=0.18; HKE –38%, P̅_St=0.40). However, the latter showed quite a high loss of the marketable DPS fraction (–36%).

The observed differences between day and night in catch proportion of undersized DPS and HKE in trawl nets equipped with and without JTED might be associated with the juveniles’ daily feeding migrations towards the sea surface at night (e.g. Savenkoff et al. 2006Savenkoff C., Savard L., Morin B., et al. 2006. Main prey and predators of northern shrimp (Pandalus borealis) in the northern Gulf of St. Lawrence during the mid-1980s, mid-1990s, and early 2000s. Can. Tech. R. Fish. & Aqua. Sci. 2639: v + 28 pp., Carpentieri et al. 2008Carpentieri P., Colloca F., Ardizzone G. 2008. Daily ration and feeding activity of juvenile hake in the central Mediterranean Sea. J. Mar. Biol. Assoc. U.K. 88: 1493-1501.), as well as to the different behaviour of the two species (e.g. swimming capability). In particular, the reduced occurrence of DPS during nocturnal hauls is associated with a reduced catch proportion of undersized specimens: from 45% less during the day to 73% less at night than the control. The scarce occurrence of HKE juveniles close to the bottom at night (Orsi Relini et al. 1997Orsi Relini L., Zamboni A., Fiorentino F., et al. 1997. Vulnerabilità luce dipendente del nasello (Merluccius merluccius) giovanile. Biol. Mar. Medit. 4: 262-268.) could affect the similar estimated probability (P_us~0.5; both gears catching equal numbers of specimens) of retaining a fish among the nocturnal hauls with and without JTEDs. Vice-versa, during the diurnal hauls, when HKE juveniles aggregate near the bottom, the JTEDs’ efficiency is clearly recognizable for the tested grids (G1-SM40 –62%, P_us~0.25; G2-ST20, –39%, P_us~0.4; G3-ST25 –50%, P_us~0.33). Even if our results need to be confirmed across seasons, oceanographic conditions, benthic communities and substrata typology, the adoption of the JTED G1-SM40 could significantly reduce the trawl catches of undersized DPS and HKE, suggesting its potential usefulness to minimize the overall discard franction. Consequently, seeking compliance with the landing obligation, the JTED G1-SM40 should be tested in commercial trawlers operating in different conditions to verify its overall sorting ability also for other species and to evaluate its potential to improve the status of Mediterranean overexploited stocks. It is worth noting that this selection device is low-cost and, according to our experience, easy to mount on commercial trawl nets.

Our findings are consistent with previous results obtained in other areas of the Mediterranean Sea, emphasizing the sorting ability of grids mounted on trawl nets. In fact, in the eastern Mediterranean demersal trawl fishery, Aydın and Tosunoğlu (2011)Aydın C., Tosunoğlu Z. 2011. Evaluation of sorting grids for deep water rose shrimp (Parapenaeus longirostris) in the Eastern Mediterranean demersal trawl fishery. J. Appl. Ichthyol. 28: 102-106. evaluated the use of sorting grids of 10- and 15-mm bar spacing, demonstrating a substantial improvement for DPS selectivity. In the same area, Aydın et al. (2011)Aydın C., Tokaç A., Aydın İ., et al. 2011. Species selectivity in the Eastern Mediterranean demersal trawl fishery using grids to reduce non-target species. J. Appl. Ichthyol. 27: 61-66. analysed the efficiency of sorting grids with 20-mm bar spacing, demonstrating a substantial separation between fish and shrimp. However, a loss of 23% and 25% of legal-sized DPS in the cod-end was recorded using 44-mm diamond and 40-mm square mesh, respectively. In the Balearic Islands (western Mediterranean), a flexible sorting grid with 15- and 20-mm bar spacing improved trawl selectivity by increasing the L₅₀for DPS and HKE and decreasing the discarded fraction (Massutí et al. 2009Massutí B.E., Ordines F., Guijarro B. 2009. Efficiency of flexible sorting grids to improve size selectivity of the bottom trawl in the Balearic Islands (western Mediterranean), with comparison to a change in mesh cod-end geometry. J. Appl. Ichthyol. 25: 153-161.). However, although some studies have explored the survival rate of discarded species in Mediterranean trawl fisheries (e.g. Revill 2012Revill A. 2012. Survival of discarded fish. A rapid review of studies on discard survival rates. DG MARE A2. Request For Services Commitment No. S12.615631. Available at: http://nsrac.org/wp-content/uploads/2012/08/EU-discard-survival-short-study-version-001.pdf, Tsagarakis et al. 2018Tsagarakis K., Nikolioudakis N., Papandroulakis N., et al. 2018. Preliminary assessment of discards survival in a multi‐species Mediterranean bottom trawl fishery. J. Appl. Ichthyol. 34: 842-849., Özvarol and Bolat 2017Özvarol Y., Bolat Y. 2017. Bottom trawl size selectivity methods in the Turkey. Sci. Pap. Ser. Manag., Econ. Engin. Agr. Rural Develop. 17: 259-262.), there is little knowledge on the mortality rates of DPS and HKE that escape through sorting grids. This aspect should be closely investigated through experimental surveys in the near future to obtain an overall assessment of the effects produced by the adoption of the grids on the stocks of the two species (Vitale et al. 2018Vitale S., Enea M., Milisenda G., et al. 2018. Modelling the effects of more selective trawl nets on the productivity of European hake (Merluccius merluccius) and deep-water rose shrimp (Parapenaeus longirostris) stocks in the Strait of Sicily. Sci. Mar. 82S1: 199-208. ).

The overexploitation of most demersal stocks in the Mediterranean (e.g. Colloca et al. 2013Colloca F., Cardinale M., Maynou F., et al. 2013. Rebuilding Mediterranean ﬁsheries: a new paradigm for ecological sustainability. Fish Fish. 14: 89-109.) increases the need to find technological solutions to improve gear selectivity, reduce discards, minimize the impacts on habitats and increase the survival rate of individuals discarded by fishers or escaping through the cod-end. In our study the engagement of local fishers was extremely useful to design appropriate sorting grids for the traditional trawl nets used by Sicilian trawlers to target DPS. Due to the increasing importance of trawling for deep-water shrimp in the Mediterranean Sea (Pinello et al. 2018Pinello D., Gee J., Accadia P., et al. 2018. Efficiency of shallow- and deep-water trawling in the Mediterranean and its implications for discard reduction. Sci. Mar. 82S1: 97-106.), the identification of ad-hoc technical tools to reduce the catch of juveniles is important for the sustainability of the fishery. In order to achieve this objective in the shrimp trawl fishery, a spatial-based approach including the closure of the nurseries of main commercial species to bottom trawling was considered a promising management measure (Maiorano et al. 2009Maiorano L., Bartolino V., Colloca F., et al. 2009. Systematic conservation planning in the Mediterranean: a flexible tool for the identification of no-take marine protected areas. ICES J. Mar. Sci. 66: 137-146., Russo et al. 2014Russo T., Parisi A., Garofalo G., et al. 2014. SMART: A Spatially Explicit Bio-Economic Model for Assessing and Managing Demersal Fisheries, with an Application to Italian Trawlers in the Strait of Sicily. PLoS ONE 9: e86222. , Colloca et al. 2015Colloca F., Garofalo G., Bitetto I., et al. 2015. The seascape of demersal fish nursery areas in the North Mediterranean Sea, a first step towards the implementation of spatial planning for trawl fisheries. PloS ONE 10: e0119590.). The GFCM recently adopted the closure of three stable nurseries of DPS and HKE in the northern sector of the Strait of Sicily (REC.CM-GFCM/40/2016). A next step in the management of the fishery could be to integrate this “drastic” measure with the adoption of new technological solutions able to consistently reduce the impact on juveniles/undersized specimens. In this context, JTED G1-SM40 could be a useful selective device for achieving the management goals of the EU (i.e. art. 14 of EU Reg. 1380/2013) and the GFCM. Although more quantitative data should be gathered to generalize the results obtained in this study, the adoption of ad hoc–designed sorting grids such as G1-SM40 may be important for improving the exploitation pattern of Mediterranean trawlers and have a positive impact on important species such as DPS and HKE.

ACKNOWLEDGEMENTSTop

The data were collected in the framework of the MINOUW project funded by the European Union, H20202-SFS-09-2014 - Towards a gradual elimination of discards in European fisheries (contract nº 634495).

REFERENCESTop

Aydın C., Tosunoğlu Z. 2011. Evaluation of sorting grids for deep water rose shrimp (Parapenaeus longirostris) in the Eastern Mediterranean demersal trawl fishery. J. Appl. Ichthyol. 28: 102-106.
https://doi.org/10.1111/j.1439-0426.2011.01897.x

Aydın C., Tokaç A., Aydın İ., et al. 2011. Species selectivity in the Eastern Mediterranean demersal trawl fishery using grids to reduce non-target species. J. Appl. Ichthyol. 27: 61-66.
https://doi.org/10.1111/j.1439-0426.2010.01605.x

Bahamon N., Sardà F., Suuronen. P. 2007. Selectivity of flexible size-sorting grid in Mediterranean multispecies trawl fishery. Fish. Sci. 73: 1231-1240.

Bellido J., Santos M., Pennino M.G., et al. 2011. Fishery discards and bycatch: solutions for an ecosystem approach to fisheries management? Hydrobiologia 670: 317-333.
https://doi.org/10.1007/s10750-011-0721-5

Brčić J., Herrmann B., De Carlo F., et al. 2015. Selective characteristics of a shark-excluding grid device in a Mediterranean trawl. Fish Res. 172: 352-360.
https://doi.org/10.1016/j.fishres.2015.07.035

Brčić J., Herrmann B., Sala A. 2017. Can a square-mesh panel inserted in front of the cod end improve size and species selectivity in Mediterranean trawl fisheries? Can. J. Fish. Aquat. Sci. 75: 704-713.
https://doi.org/10.1139/cjfas-2017-0123

Caddy J.F. 1990. Options for the regulation of Mediterranean demersal fisheries. Nat. Res. Model. 4: 427-475.
https://doi.org/10.1111/j.1939-7445.1990.tb00219.x

Carpentieri P., Colloca F., Ardizzone G. 2008. Daily ration and feeding activity of juvenile hake in the central Mediterranean Sea. J. Mar. Biol. Assoc. U.K. 88: 1493-1501.
https://doi.org/10.1017/S0025315408001859

Colloca F., Cardinale M., Maynou F., et al. 2013. Rebuilding Mediterranean ﬁsheries: a new paradigm for ecological sustainability. Fish Fish. 14: 89-109.
https://doi.org/10.1111/j.1467-2979.2011.00453.x

Colloca F., Garofalo G., Bitetto I., et al. 2015. The seascape of demersal fish nursery areas in the North Mediterranean Sea, a first step towards the implementation of spatial planning for trawl fisheries. PloS ONE 10: e0119590.
https://doi.org/10.1371/journal.pone.0119590

Colloca F., Scarcella G., Libralato S. 2017. Recent Trends and Impacts of Fisheries Exploitation on Mediterranean Stocks and Ecosystems. Front. Mar. Sci. 4: 244.
https://doi.org/10.3389/fmars.2017.00244

Dereli H., Aydin C., Kebapçioğlu T., et al. 2016. Selectivity of commercial and experimental cod-ends for the demersal trawl fishery of the deep-water rose shrimp, Parapenaeus longirostris (Lucas, 1846), in the Aegean Sea. Crustaceana 89: 477-493.
https://doi.org/10.1163/15685403-00003532

Di Lorenzo M., Sinerchia M., Colloca F. 2018. The North sector of the Strait of Sicily: a priority area for conservation in the Mediterranean Sea. Hydrobiologia 821: 235-253.
https://doi.org/10.1007/s10750-017-3389-7

Fiorentini L., Sala A., Hansen K., et al. 2004. Comparison between model testing and full-scale trials of new trawl design for Italian bottom fisheries. Fish. Sci. 70: 349-359.

Fiorentino F., Ben Hadj Hamida O., Ben Meriem S., et al. 2013. Synthesis of information on some demersal crustaceans relevant for fisheries target species in the south-central Mediterranean Sea. GCP/RER/010/ITA/MSM-TD-32. MedSudMed Tech. Doc. 32: 1-120.

Fryer R.J., Zuur A.F., Graham N. 2003. Using mixed models to combine smooth size selection and catch-comparison curves over hauls. Can. J. Fish. Aquat. Sci. 60: 448-459.
https://doi.org/10.1139/f03-029

Holst R., Revill A.S. 2009. A simple statistical method for catch comparison studies. Fish. Res. 95: 254-259.
https://doi.org/10.1016/j.fishres.2008.09.027

Kaykaç H., Tokaç A., Özbilgin H. 2009. Selectivity of commercial, larger mesh and square mesh trawl cod-ends for deep water rose shrimp Parapenaeus longirostris (Lucas, 1846) in the Aegean Sea. Sci. Mar. 73: 597-604.
https://doi.org/10.3989/scimar.2009.73n3597

Lleonart J., Maynou F. 2003. Fish stock assessments in the Mediterranean: State of the art. Sci. Mar. 67: 37-49.
https://doi.org/10.3989/scimar.2003.67s137

Lucchetti A., Punzo E., Virgili M. 2016. Flexible Turtle Excluder Device (TED): an effective tool for Mediterranean coastal multispecies bottom trawl fisheries. Aquat. Living. Resour. 29: 201.
https://doi.org/10.1051/alr/2016016

Maiorano L., Bartolino V., Colloca F., et al. 2009. Systematic conservation planning in the Mediterranean: a flexible tool for the identification of no-take marine protected areas. ICES J. Mar. Sci. 66: 137-146.
https://doi.org/10.1093/icesjms/fsn148

Massutí B.E., Ordines F., Guijarro B. 2009. Efficiency of flexible sorting grids to improve size selectivity of the bottom trawl in the Balearic Islands (western Mediterranean), with comparison to a change in mesh cod-end geometry. J. Appl. Ichthyol. 25: 153-161.
https://doi.org/10.1111/j.1439-0426.2009.01225.x

Maynou F., Gil M.D.M., Vitale S., et al. 2018. Fishers’ perceptions of the European Union discards ban: perspective from south European fisheries. Mar. Policy 89: 147-153.
https://doi.org/10.1016/j.marpol.2017.12.019

Milisenda G., Vitale S., Massi D., et al. 2017. Spatio-temporal composition of discard associated with the deep water rose shrimp fisheries (Parapenaeus longirostris, Lucas 1846) in the southcentral Mediterranean Sea. Med. Mar. Sci. 18: 53-63.
https://doi.org/10.12681/mms.1787

Morrissey M.T., Almonacid S. 2005. Rethinking technology transfer. J. Food Eng. 67: 135-145.
https://doi.org/10.1016/j.jfoodeng.2004.05.057

Orsi Relini L., Zamboni A., Fiorentino F., et al. 1997. Vulnerabilità luce dipendente del nasello (Merluccius merluccius) giovanile. Biol. Mar. Medit. 4: 262-268.

Özvarol Y. 2016. Size selectivity of sorting grid for eight fish species in the Gulf of Antalya, North eastern Mediterranean Sea. Iran. J. Ichthyol. 3: 294-303.

Özvarol Y., Bolat Y. 2017. Bottom trawl size selectivity methods in the Turkey. Sci. Pap. Ser. Manag., Econ. Engin. Agr. Rural Develop. 17: 259-262.

Pinello D., Gee J., Accadia P., et al. 2018. Efficiency of shallow- and deep-water trawling in the Mediterranean and its implications for discard reduction. Sci. Mar. 82S1: 97-106.
https://doi.org/10.3989/scimar.04749.22A

Ragonese S., Zagra M., Di Stefano L., et al. 2001. Effect of cod-end mesh size on the performance of the deep-water bottom trawl used in the red shrimp fishery in the Strait of Sicily (Mediterranean Sea). Hydrobiologia 449: 279-291.
https://doi.org/10.1007/978-94-017-0645-2_31

Revill A. 2012. Survival of discarded fish. A rapid review of studies on discard survival rates. DG MARE A2. Request For Services Commitment No. S12.615631. Available at:
http://nsrac.org/wp-content/uploads/2012/08/EU-discard-survival-short-study-version-001.pdf

Russo T., Parisi A., Garofalo G., et al. 2014. SMART: A Spatially Explicit Bio-Economic Model for Assessing and Managing Demersal Fisheries, with an Application to Italian Trawlers in the Strait of Sicily. PLoS ONE 9: e86222.
https://doi.org/10.1371/journal.pone.0086222

Sala A., Lucchetti A., Perdichizzi A., et al. 2015. Is square-mesh better selective than larger mesh? A perspective on the management for Mediterranean trawl fisheries. Fish. Res. 161: 182-190.
https://doi.org/10.1016/j.fishres.2014.07.011

Sala A., Herrmann B., De Carlo F., et al. 2016. Effect of Cod-end Circumference on the Size Selection of Square-Mesh Codends in Trawl Fisheries. PLoS ONE 11: e0160354.
https://doi.org/10.1371/journal.pone.0160354

Santiago J.L., Ballesteros M.A., Chapela R., et al. 2015. Is Europe ready for a results-based approach to fisheries management? The voice of stakeholders. Mar. Policy 56: 86-97.
https://doi.org/10.1016/j.marpol.2015.02.006

Sardà F., Bahamón N., Sardà-Palomera F., et al. 2005. Commercial testing of a sorting grid to reduce catches of juvenile hake (Merluccius merluccius) in the western Mediterranean demersal trawl fishery. Aquat. Living Resour. 18: 87-91.
https://doi.org/10.1051/alr:2005010

Savenkoff C., Savard L., Morin B., et al. 2006. Main prey and predators of northern shrimp (Pandalus borealis) in the northern Gulf of St. Lawrence during the mid-1980s, mid-1990s, and early 2000s. Can. Tech. R. Fish. & Aqua. Sci. 2639: 1-28.

Sola I., Maynou F. 2018. Assessment of the relative catch performance of hake, red mullet and striped red mullet in a modified trawl extension with T90 netting. Sci. Mar. 82S1: 19-26.
https://doi.org/10.3989/scimar.04711.04A

Stergiou K.I., Moutopoulos D.K., Armenis G. 2009. Perish legally and ecologically: the ineffectiveness of the minimum landing sizes in the Mediterranean Sea. Fish. Manag. Ecol.16: 368-375.
https://doi.org/10.1111/j.1365-2400.2009.00672.x

Suuronen P., Sardà F. 2007. By-catch reduction techniques in European fisheries: traditional methods and potential innovations. In: Kennelly S.J. (ed.), By-catch Reduction in the World’s Fisheries, Springer, Dordrecht, pp. 37-74.
https://doi.org/10.1007/978-1-4020-6078-6_3

Tokac A., Herrmann B., Aydın C., et al. 2014. Predictive models and comparison of the selectivity of standard (T0) and turned mesh (T90) codends for three species in the Eastern Mediterranean. Fish. Res. 150: 76-88.
https://doi.org/10.1016/j.fishres.2013.10.015

Tsagarakis, K., Carbonell A., Brčić J., et al. 2017. Old Info for a New Fisheries Policy: Discard Ratios and Lengths at Discarding in EU Mediterranean Bottom Trawl Fisheries. Front. Mar. Sci. 4: 99.
https://doi.org/10.3389/fmars.2017.00099

Tsagarakis K., Nikolioudakis N., Papandroulakis N., et al. 2018. Preliminary assessment of discards survival in a multi‐species Mediterranean bottom trawl fishery. J. Appl. Ichthyol. 34: 842-849.
https://doi.org/10.1111/jai.13691

Vasilakopoulos P., Maravelias C.D., Tserpes G. 2014. The Alarming Decline of Mediterranean Fish Stocks. Curr. Biol. 24: 1643-1648.
https://doi.org/10.1016/j.cub.2014.05.070

Veiga V., Pita C., Rangel M. et al. 2016. The EU landing obligation and European small-scale fisheries: What are the odds for success? Mar. Pol. 64: 64-71.
https://doi.org/10.1016/j.marpol.2015.11.008

Vitale S., Enea M., Milisenda G., et al. 2018. Modelling the effects of more selective trawl nets on the productivity of European hake (Merluccius merluccius) and deep-water rose shrimp (Parapenaeus longirostris) stocks in the Strait of Sicily. Sci. Mar. 82S1: 199-208.
https://doi.org/10.3989/scimar.04752.03A

Wood S.N. 2006. Generalized additive models: an introduction with R. Chapman & Hall, Boca Raton, Florida, U.S.A., 416 pp.
https://doi.org/10.1201/9781420010404

Zuur A.F., Ieno E.N., Smith G.M. 2007. Analysing Ecological Data. Springer-Verlag, New York, 672 pp.
https://doi.org/10.1007/978-0-387-45972-1